Ignition assembly for perforated cylindrical charge



Oct. 11, 1960 w. A. SHOW ETAL 2,955,535

IGNITION ASSEMBLY FOR PERFORATED CYLINDRICAL CHARGE Filed May 28. 1958 IN VEN TORS.

\VlLLlA/A A. suow Fig. I: By NOR/AAN J. \VlLKAiTI5 JOHN A. IAILLER ATTORNEVE Patented Oct. 11, 1960 IGNITION ASSEMBLY FOR PERFORATED (IYLINDRICAL CHARGE Filed May 2a, 1958, Ser. No. 738,344 '6 Claims. Cl. 102-911 ammonium nitrate consolidated charges are exceedingly difficult to ignite. Thus, previous attempts to utilize ammonium nitrate in solid gas generating charges have not been completely satisfactory because no reliable means have heretofore been found for their ignition. For this reason, such charges are generally based on more expensive and less desirable materials such as nitroguanidine, guanidine nitrate, nitrocellulose usually compounded with nitroglycerin, and ammonium perchlorate.

It is, therefore, an object of this invention to provide a solid gas generating assembly overcoming the disadvantages of the prior art. Another object of this invention is to provide an improved ignition assembly for solid gas generating charges. A more specific object of this invention is to provide an assembly capable of reliably igniting ammonium nitrate gas generating charges as well as other types of solid gas generating charges. Other objects will be apparent when the following detailed description is read in connection with the accompanying drawing in which:

Figure 1 is a longitudinal sectional view of an ignition assembly illustrating a preferred embodiment of the present invention; and

Figure 2 is a cross-sectional view taken along the line II-II of Figure 1.

These objects are accomplished in accordance with this invention, generally speaking, by providing a consolidated gas generating charge having a central perforation and an igniter positioned within the perforation so as to impinge a concentrated flame upon the surface of the perforation. More specifically, this invention contemplates a gas generating charge containing as the main fuel a large grain, preferably of consolidated ammonium nitrate, having a central perforation and an ignition assembly positioned within the central perforation near one end of the grain and having its longitudinal axis substantially perpendicular to the longitudinal axis of the grain. In order to insure the transmission of the ignition stimuli to other portions of the grain, a pyrotechnic tape is affixed to the area of the grain in the neighborhood of the ignition assembly and extends to the external lateral surface of the grain. The ignition assembly is housed in a suitable container which is open at both ends. This housing, which may be a paper tube, phenol formaldehyde resin, or the like, serves as a lateral inhibitor for the igniter. Thus, upon ignition, flame and hot gases emit from either end of the igniter directly upon the pyrotechnic tape covering the surface of the perforation.

The ignition assembly consists primarily of an inorganic granular perchlorate charge bound in a plastic matrix. While ammonium perchlorate is preferred in the igniter charge, other inorganic perchlorates, such as potassium perchlorate, sodium perchlorate, and the like, can also be utilized. This charge is preferably bound in a matrix formed from a plasticized polyvinyl chloride plastisol. However, other materials, such as nitrocellulose, nitrostarch, polyvinyl acetate, and the like can be used as the binder. The igniter is actuated by an electric squib or other suitable deflagrating device embedded therein. In those instances where a relatively small squib is utilized, a pyrotechnic booster, such as a thermit type charge of ferric oxide mixed with aluminum or zirconium, can be used.

The ignition assembly can be positioned within the central perforation of the main charge by any suitable means. While it is preferred to utilize a stainless steel or other metallic hanger, any device capable of maintaining the ignition assembly in an operable position can be employed.

The pyrotechnic tape which is affixed to the surface of the grain by a suitable adhesive or other mechanical means is formed 'of cloth, such as gauze or cotton, wool, linen, or the like. This fabric strip is provided with a suitable flame propagating material or mixture before it is positioned on the grain. When the flame propagating material contains granular constituents, a suitable binder is also included. This tape can be impregnated with readily ignitable mixtures of ammonium or potassium perchlorate, potassium nitrate, sulfur, and charcoal. Other pyrotechnic mixtures, such as ferric oxide, sulfur, aluminum, black powder mixtures, and the like, can also be used as the impregnant. These strips of tape are attached to the surface of the grain within the perforation and extend to the external lateral surface of the grain. To insure uniform ignition of the external surface of the grain, an additional pyrotechnic tape is wound about the perimeter of the gas generating charge and over the strips of tape originating from the central perforation. This peripheral tape can be held in position by a suitable adhesive or by a retaining ring.

In operation, the electric squib initiates the booster thermit charge or the igniter mix directly. The flame from the igniter mix is directed upon the internal wall of the gas generating charge at points covered by the pyrotechnic tape. This insures the ignition of the main charge within its perforation and the flame is rapidly and uniformly transmitted to the peripheral surface of the grain by means of the pyrotechnic tapes. This assembly can be housed in any suitable type cartridge.

In order to more fully explain and further clarify the invention, reference is made to the drawing for a preferred embodiment thereof. Unless otherwise specified, compositions of the various formulations are expressed in parts by weight.

In this embodiment, the main gas generating charge consists of a cylindrical grain 1, having a density of approximately 1.3 and weighing about 8 pounds. This charge consists essentially of ammonium nitrate and a synthetic rubber binder therefor. This grain has an outside diameter of approximately 5 inches, a central longitudinal perforation 2 of approximately 2 inches and about 6 inches long. A 1 ounce charge 3 of 70% ammonium perchlorate in a polyvinyl chloride plastisol matrix is contained in a cylindrical paper housing 4. A squib 5 charged with lead thiocyanate and potassium chlorate and provided with lead wires 6 is imbedded in ignition mix 3. A flame intensifying charge 7, weighing approximately 1.5 grams and composed of about 30% zirconium and 70% ferric oxide, is positioned at the base of the squib. In this embodiment, the igniter assembly is maintained in position by means of stainless steel fixture 8. The wall of the grain within the perforation 2 is provided with at least 2 pyrotechnic strips 9. These strips which are approximately of an inch wide and 7 inches long are impregnated with about 3 grams of a pyrotechnic mixture containing 55% ammonium perchlorate, 20% potassium nitrate, 13% sulfur, 2% charcoal and polyvinyl acetate as a binder. As shown in the drawing, these strips extend from the locus of the igniter assembly to the external surface of the main gas generating charge which 'is provided with an additional'pyrotechnic tape 10. This gauze tape, which is about 2 inches wide and. 16 inches long carries about grams of a mixture of 20% ammonium perchlorate, 50% potassium nitrate, 10% sulfur and 20% polyvinyl acetate as a binder. As shown in the drawing, this-tape is wound about the external periphery of the main fuel charge, thus providing uni-form peripheral ignition.

This cartridge, upon initiation of the squib, ignited readily and burned for approximately 15 seconds providing substantially uniform'pressure throughout its burning eriod.

p While the above embodiment was directed specifically to an ammonium nitrate gas generating charge, it will be readily appreciated that this same ignition system can be utilized with advantage in connection with other gas generating compositions. It is also evident that various other modifications can be made without departing from the scope of the present invention. For example, various types of pyrotechnic tapes can be utilized for the transmission of the ignition stimuli and if a sufiicient number of tapes are inserted within the perforation, the external tape about the charge can be eliminated. Also, the ignition assembly may be housed and positioned by any suitable means.

ince variations in the specific embodiment may be made within the spirit and scope of this invention, the detailed description is not to be considered as lim-itative except in the light of the appended claims.

What is claimed is:

l. A fuel charge for a gas generating device comprising as a main fuel a cylindrical grain of a gas generating composition having at least one longitudinal perforation and a substantially cylindrical igniter for said fuel charge positioned within the perforation, the entire curved surface of the igniter being laterally inhibited, the longitudinal axis of the igniter being at substantially right angles to the longitudinal axis of the main fuel charge, strips of a pyrotechnic webbing aflixed to the surface of the grain in the perforation opposite at least one end of the igniter, said strips extending along the surface of the perforation to one end of the grain and over that end of the grain to the external lateral wall thereof.

2. A fuel charge for a gas generating charge comprising as a main fuel a cylindrical grain of a gas generating composition having at least one longitudinal perforation and a substantially cylindrical igniter for said fuel charge positioned within the perforation closer to one end of the grain than the other, the entire curved surface of the igniter being laterally inhibited, the longitudinal axis of the igniter being at substantially right angles to the longitudinal axis of the main fuel charge, strips of a pyrotechnic webbing affixed to the surface of the grain in the perforation opposite at least one end of the igniter, said strips extending along the surface of the perforation to one end of the grain and over that end of the grain to the external lateral wall thereof, and

4 a pyrotechnic tape affixed about the perimeter of the gas generating charge and over the strips of pyrotechnic webbing.

3. A fuel charge for a gas generating device comprising as the main fuel a cylindrical grain of a consolidated ammonium nitrate gas generating composition having at least one longitudinal perforation and a substantially cylindrical'igniter for said fuel charge positioned within the perforation, the longitudinal axis of the igniter being substantially perpendicular to the longitudinal axis of the main fuelcharge, the entire curved surface of the igniter being laterally inhibited, the igniter comprising a consolidated charge of an inorganic perchlorate in a plastic matrix and having imbedded therein an electric squib together with a pyrotechnic booster charge adapted to be ignited by the squib, strips of a pyrotechnic webbing affixed to the surface of the grain in the perforation opposite at least one end of the igniter, said strips extending along the surface of the perforation to one end of the grain and over that end of the grain to the external lateral wall thereof.

4. An ignition means for a centrally perforated cylindrical gas generating charge comprising an electric squib, a pyrotechnic booster charge adapted to be ignited by the squib, the squib and the booster being imbedded in a substantially cylindrical consolidated charge of about percent of an inorganic perchlorate and about 30 percent polyvinyl chloride plastisol, the entire curved surface of the consolidated charge being inhibited, the longitudinal axis of the consolidated charge being substantially perpendicular to the longitudinal axis of the perforation, the plastisol being in the form of a matrix for the ammonium perchlorate, a pyrotechnically impregnated webbing affixed to the surface of the perforation in the gas. generating charge adjacent the ignition means and extending out of the perforation and over one end of the gas generating charge.

5. A fuel charge for a gas generating device comprising as a main fuel a cylindrical grain of a gas generating composition having at least one longitudinal perforation, and a substantially cylindrical igniter for said fuel charge positioned within the perforation closer to one end of the grain than the other, the entire cylindrical surface of the igniter being inhibited, the longitudinal axis of the igniter being at substantially right angles to the longitudinal axis of the main fuel charge, the igniter comprising a consolidated charge of an inorganic perchlorate in a plasticmatrix and having imbedded therein a squib, strips of pyrotechnic Webbing afiixed to the surface of the grain opposite at, least one end of the igniter and extending along the surface of the perforation and over the adjacent end of the cylindrical grain.

6. The fuel charge of claim 5 in which the squib is charged with a mixture of potassium chlorate and lead thiocyanate, the pyrotechnic booster is composed of about 30 percent by weight zirconium and about 70 percent by weight ferric oxide, and the pyrotechnic strips consist of a gauze impregnated with a mixture of '55 percent ammonium perchlorate, 20 percent potassium nitrate, 13 percent sulfur, 10 percent polyvinyl acetate, and 2 percent charcoal. 1

References Cited in the file of this patent UNITED STATES PATENTS 2,410,801 Audrieth Nov. 12, 1946 2,697,325 Spaulding Dec. 12, 1954 2,743,580 .Loeb May 1, 1956 

